As a method for producing (meth)acrylic acid or (meth)acrolein, there is a method for subjecting propylene, propane, isobutylene to catalytic gas phase oxidation with an oxygen-containing gas in the presence of a catalyst to obtain (meth)acrolein, and further subjecting (meth)acrolein to catalytic gas phase oxidation to obtain a reaction gas including (meth)acrylic acid.
Here, (meth)acrolein means “acrolein or methacrolein”, and (meth)acrylic acid means “acrylic acid or methacrylic acid”.
In the above-described method, a catalyst for industrially producing (meth)acrylic acid or (meth)acrolein is a composite metal oxide, and a catalytic gas phase oxidation is continuously carried out while supplying a raw material and an oxygen-containing gas such as air in the presence of the catalyst at all times of normal running.
Where propylene, propane, isobutylene and (meth)acrolein, which are raw materials or intermediate products of (meth)acrylic acid or (meth)acrolein are blended with oxygen at a predetermined ratio, an explosive composition is formed which may result in an explosion by a firing source such as a high temperature substance or electric spark. Therefore, in order to protect production facilities from such an explosion and to automatically stop the production facilities safely, an automatic emergency stop apparatus (an interlock system) is installed, which discharges flammable gases in the apparatus out of the system by stopping supply of a flammable raw material and blowing inert gases such as a nitrogen gas, steam, etc., into the production facilities, when the explosive composition is formed.
When the running is re-started after such an emergent shutdown, or after a shutdown for a periodic inspection, there are cases where the reaction activity of a catalyst and selectivity of a target product are lowered.
In JP-A-2002-53519, a safe start-up method is disclosed in a catalytic gas phase oxidation reactor. However, no description is given of solving a problem due to which the reaction activity of a catalyst and selectivity of a target product after re-start of the running are lowered.